1. Field of the Invention
The present invention relates to orthopedic braces.
2. Description of the Related Art
Many knee braces restrain the wearer's knee against harmful motions. Many of these knee braces provide such restraint while at the same time guiding the wearer's knee along a natural range of motion. Accordingly, many knee brace hinges attempt to mimic the natural motion of the knee. Some of these designs include monocentric hinges, polycentric hinges, four-bar-linkage hinges, and cam hinges. Each of these designs has a unique range of motion.
In general, when viewed in the sagittal plane, the human knee moves in a slide-and-glide fashion in which the femur partially rolls back posteriorly on the tibia as the knee flexes. The posterior roll back of the femur is most pronounced when the knee flexes beyond 90 degrees from full extension. One problem common to each of the hinge designs mentioned above is that natural knee motion varies from person to person. In fact, natural knee motion may even vary for an individual depending on the type of activity in which he or she engages. Because of these variations in natural knee motion, a knee brace may apply undesired forces to the wearer's knee as a result of the mismatch between hinge motion and natural knee motion.
Some knee brace hinge designs attempt to solve the previously mentioned problems by allowing the pivot point of the hinge to float in the anterior-posterior direction and/or the superior-inferior direction. These hinges have more than one degree of freedom and can follow more than one path of motion. The hinge pivot point is capable of changing position in order to match the instantaneous pivot point of the knee at any given time. Some examples of these types of hinges are described in U.S. Pat. Nos. 5,063,916 and 5,074,290. One drawback to these hinge designs is that the flexibility in movement renders the hinges unable to restrain some of the harmful motions to which the wearer's knee may be subjected.
In general, the knee is most vulnerable to injury when the leg is near full extension. In this position, the anterior cruciate ligament (ACL) is at its greatest tension. The ACL acts to prevent the tibia from moving anteriorly relative to the femur. To protect the ACL from injury, a knee brace restrains this type of motion (anterior movement of the tibia relative to the femur). The ACL is also vulnerable to injury from hyperextension and hyperflexion. Therefore, a given knee brace is preferably capable of limiting the degree of extension and flexion of the knee. When the knee is bent sufficiently away from full extension, the ACL becomes lax and is much less vulnerable to injury. In addition, as the knee flexes much of the anterior-posterior motion of the knee becomes controlled by muscle forces rather than ligament restraint.
A typical knee brace protects the medial and lateral collateral ligaments (MCL and LCL) by preventing varus and valgus bending of the knee. Such bending may occur from impacts to the sides of the knee.